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lipids - Dongguk€¦ · lipids Any of a group of Nonpolar, hydrophobic substances that in general...
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Transcript of lipids - Dongguk€¦ · lipids Any of a group of Nonpolar, hydrophobic substances that in general...
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lipids
Any of a group of Nonpolar, hydrophobicsubstances that in general are soluble in organic solvents such as diethyl ether, petroleum ether, acetone, chloroform, benzene, CCl4, but are not soluble in water.
Definition
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Includes fats: solid at room temperature
oils: liquid at room temperature Definition based on physical properties
TriglyceridesFatty AcidsPhospholipids
Terpenes/TerpenoidsSteroidsWaxes
Primary topics for Food Science
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Energy Source Carrier of Fat Soluble Vitamins Main Flavor Source of Foods Hormone and Cell Structure Nerve System Thermal Insulation of Body Mouth Feeling Texture of Foods Emulsifying Agents Mold Releasing and Anti-spattering Agent
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Hydrolysis products of lipids Carboxylic acid RCOOH No of Carbon: even Could have double bond
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Saturated or unsaturated◦ w/ or w/o double bonds
polyunsaturated fatty acids: 2 or more double bonds
Higher/lower fatty acid◦ No of carbons 4~12: lower◦ 14~ : higher
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R-groups on fatty acid chains are generally linear hydrocarbons, e.g.
which may be more simply represented as
CO
- O -CH3CH2 CH2 CH2 CH2 CH2 CH2 CH2
CH2 CH2 CH2 CH2 CH2 CH2 CH2
CO
- O -
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Many R groups are alkane groups◦ single bonds only◦ these are called saturated fatty acids
Other R groups are alkene groups◦ 1 - 6 double bonds◦ fatty acids with one double bond are called
monounsaturated◦ fatty acids with two or more double bonds are
called polyunsaturated
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Fatty acid chains represented using numbering system:
N:M
Chemists number carbons from chemically most reactive end
E.g. 12:0
consists of 12 carbons with no double bonds.
number of carbons inchain
number of C=Cdouble bonds in chain
CO
- O -1
2
3
4
5
6
7
8
9
10
11
12
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The symbol followed by the carbon number is used to indicate the position of the double bond
E.g. 18:19
consists of 18 carbons with 1 double bond located between the 9th and 10th carbon.
1812 14 16
11 13 15 17
101 3 5 7 9
2 4 6 8
CO
- O -
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Scientists in the medical and nutrition community often number carbons from the opposite (tail) end◦ this nomenclature uses to denote the double bond position
E.g. the molecule
an be designated as 18:3 9,12,15, or as18:3 1812
14
16
11
13 15
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10CO
- O -1
2
3
4
5
6
7
8
9
18 121416
11131517
10CO
- O -1
2
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5
67
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9
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Recall double bonds can be cis or trans
E.g.
C = C
cis
R’ R”
H HC = C
transR”H
HR’
CO
- O -cis
CO
- O -trans
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Prefix indicates number of carbons Suffix indicates degree of unsaturation◦ “-anoic” if saturated◦ “-enoic” if monounsaturated◦ “-adienoic” if two double bonds◦ “-atrienoic” if three double bonds◦ “-atetraenoic” if four double bonds
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Saturated Fatty Acids
CH3 CH2 CH2 CH2 CH2 CH2 CH2 C OHO
1245678 3
Octanoic Acid
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Unsaturated Fatty Acids
CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 C OHO
1245678 3
CH3 CH2 CH2 CH2 CH2 CH2 CH2 C OHO
1245678 3
3 - Octenoic Acid
3, 6 - Octadienoic Acid
Short hand: 8:1 (3)
8:2 (3,6) 1
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Cis 9 - Octadecenoic Acid (oleic)
Trans 9 - Octadecenoic Acid (elaidic acid)
OCH3(CH2)7 C C (CH2)7 C OH
HH
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OCH3(CH2)7 C C (CH2)7 C OH
H
H
Cis And Trans Fatty Acids
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Abbreviation Systematic Name Common Name Symbol
4:0 Butanoic Butyric B
6:0 Hexanoic Caproic H
8:0 Octanoic Caprylic Oc
10:0 Decanoic Capric D
12:0 Dodecanoic Lauric La
14:0 Tetradecanoic Myristic M
16:0 Hexadecanoic Palmitic P
18:0 Octadecanoic Stearic St
18:1 9-Octadecenoic Oleic O
18:2 9,12-Octadecadienoic Linoleic L
18:3 9,12,15-Octadecatrienoic Linolenic Ln
20:0 Eicosanoic Arachadic A
20:4 5,8,11,14-Eicosatetraenoic Arachadonic An
22:1 13-Docosenoic Erucic Ei
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20:5 Eicosapentaenoic acid (EPA) 5,8,11,14,17- Eicosapentaenoic acid
22:6 Docosahexaenoic acid (DHA) 4,7,10,13,16,19- Docosahexaenoic acid
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Shorter-chain fatty acids (C4 - C12) are found only in coconut/palm oils and in bovine milk
Fatty Acid4:06:08:0
10:012:014:016:0
Flavor Characteristicsrancidrancid
musty, rancid, soapysoapysoapysoapy
Threshold Concentration
(mg/kg)
5085200
> 400> 400> 400
not detectable
the shorter the chain, the stronger the flavor
(Belitz and Grosch, 1999; © Springer-Verlag.)
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RCOOH◦ Stabilized by H-bond
Structure and MP◦ MP α No of carbon◦ α 1/No of double bonds
Solubility◦ α 1/No of carbon
Absorption of UV◦ Use for measurements of peroxidation of FA : Conjugated
formation
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•Food fats/oils are primarily triacylglycerols, commonly called triglycerides.–3 fatty acid chains on a glycerol backbone
HO - C
O
- R1
3 fatty acids
+
C
O
- R3HO -
HO - C
O
- R2
OH
OH
OHglycerol
HC
H2C
H2C
OC
COCO
O
O
O
- R1
triacylglycerol
= - R2
- R3
HC
H2C
H2C
–One chiral carbon with 1-3 acyl groups–simpler stereochemistry than sugars–more possible substituents
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Triglycerides have one chiral center:
C
CH2
CH2
H
C
O
O R1
C
O
O R3
OC
O
R2
sn-1
sn-2sn-3
–fatty acids located at sn-1, sn-2 and sn-3 positions–“sn” means “stereospecific numbering”
OCOR2
CH2OCOR3
CH2OCOR1
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Palmitic acid:◦ Tripalmitoyglycerol◦ PPP
1. stearic acid, 2. oleic acid, 3. myristic acid: ◦ sn-StOM
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Cocoa butter◦ ~ equal C16:0,
C18:0, C18:1◦ sn-2 primarily
unsat’d◦ sn-1,3 largely sat’d
0102030405060708090
mol
e %
of f
atty
aci
d gr
oups
C16:0 C18:0 C18:1 C18:2
fatty acid constituent
sn-1 sn-2 sn-3 all
– Coconut, palm oil rich in C8:0-C16:0
S
S
U
66%
U
S
U
20%
(Belitz and Grosch, 1999; © Springer-Verlag.)
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Peanut Oil◦ ~40% oleic;
40%linoleic◦ sn-2 largely unsat’d
0
10
20
30
40
50
60m
ole
% o
f fat
ty a
cid
grou
ps
C16:0 C18:0 C18:1 C18:2
fatty acid constituent
sn-1 sn-2 sn-3 all
S
U
U
U
U
U
–Soybean oil similar
(Belitz and Grosch, 1999; © Springer-Verlag.)
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Pig Fat (Lard)◦ ~ equal C16:0, C18:0,
C18:1◦ sn-2 largely sat’d◦ sn-1 both sat’d &
unsat’d◦ sn-3 largely unsat’d
0
10
20
30
40
50
60
70
80
C16:0 C18:0 C18:1 C18:2
fatty acid constituent
sn-1 sn-2 sn-3 all
S
U
S
U
U
S
U
S
U
36%29% 12%
U
U
U
15%
(Belitz and Grosch, 1999; © Springer-Verlag.)
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Phospholipids Glycerophospholipids◦ Ester of Phosphatic acid
Major components of cell membrane◦ 1 polar head, 2 hydrocarbon tails : amphoteric
substance → emulsifier ◦ Lecithin (phosphatidylcholine)
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Glycerol backbone◦ 2 groups fatty acid substituents◦ Third group phosphate derivative
OC
CO
O
O
O
O PO
OX -
E.g. X = - (CH2)2 - N - CH3
CH3
CH3
+
phosphatidylcholine30
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Phosphatide “headgroup” is polar, charged◦ hydrophilic
Fatty acid “tails” are nonpolar◦ hydrophobic
Molecule thus has split character◦ amphiphilic
•Molecules are surface active
–Sit between hydrophilic and hydrophobic phases P
X
oil
water
PX
air
water
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Lipids + sugar Cell Membrane components Monogalactoxyldiacylglycerol (MGDC) Digalactoxyldiacylglycerol (DGDG)
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Cell Membrane components Ceremide: sphingosine + fatty acid Sphingoglycolipid: ceremide + phosphoric
acid, or sugars◦ Sphingomyelin: ceremide + phosphoric acid +
choline◦ Cerebroside: ceremide + sugar (galactose etc.)
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TransCelebroside: Gal
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Waxes◦ Esters of long chain fatty acids and long chain alcoholsE.g. beeswax
CH3(CH2)nCOCH2(CH2)mCH3
n = 24 or 26; m = 28 or 30
◦ solid, impermeable to water Important in fruits:
◦ Natural protective layer in fruits, vegetables, etc.◦ Added in some cases for appearance and protection.
O
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Not digestible In animals ◦ Bee wax (蜜蠟): Myricyl palmitate melissyl alcohol(C30H61OH) + palmitic acid◦ Whale wax (鯨蠟): Cetyl palmitate, Cetyl alcohol(C16H33OH) + palmitic acid
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Steroid Sterols : 4 condensed rings, alcoholic -OH
at C-3 zoosterols◦ cholesterol : biosynthesis from squalene, sex
hormone, precursor of bile acid phytosterols ◦ Sitosterol, campesterol, stigmasterol
mycosterols◦ Ergosterol
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Cholesterol
Sitosterol
Terpenes/TerpenoidsConsist of isoprene units
ExamplesEssential oils:
e.g. limonenepinenementholC = C
CH3
C = C
H
HH H
H
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Fat Soluble Vitamins
Vitamin A
CH2 OHCH3 CH3
CH3
CH3H3C
12
34
5
67
89
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Vitamin D2
Vitamin EHO
CH 2
HH
H 3 CH 3 C CH 3
CH 3
CH 3
OR1
R2
HO
R3
CH3(CH2CH2CH2CH2)2CH2CH2CH2CH(CH3)2
CH3
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